The invention relates to a pointer instrument, in particular in a motor vehicle, having two pointer shafts which can each be driven by a separate pointer drive, and two scales which are arranged concentrically with respect to one another and are each intended for one pointer.
Pointer instruments of the abovementioned type are generally known and customary. Because, in order to make the expenditure acceptable and for reasons of space, the two pointer drives can only be arranged one next to the other, the pointer shafts usually extend at a distance from one another. Accordingly, the ends of the pointers move over eccentric arcs so that the scales also have to be arranged eccentrically with respect to one another. The nonconcentric arrangement of the scales leads, however, to the display instrument often being undesirably being made larger, and gives rise to mutual overlapping of the two scales.
From clocks it is known to embody a pointer shaft as a hollow shaft and to arrange a second pointer shaft in this hollow shaft. This makes it possible to provide one pointer on each of the pointer shafts, the pointers being able to pivot over scales which are arranged concentrically with respect to one another.
With pointer instruments, for motor vehicles, it is already known, in such pointer shafts which are nested one in the other, to drive the pointer shaft which is embodied as a hollow shaft by means of two gear wheels, from a pointer drive which drives laterally with respect to [lacuna] the inner pointer shaft. As a result, the pointer instrument can be provided with two pointers which are aligned concentrically with respect to one another, can pivot over concentric scales and can be driven independently of one another. However, the construction of such a gear wheel mechanism is costly and reduces the dynamics of a display because it requires two gear wheels to be additionally driven by the pointer drive, and relatively high frictional forces occur. Furthermore, it is not possible to illuminate the pointer of the hollow shaft by injecting light into the pointer.
The invention is based on the problem of constructing a pointer instrument of the type mentioned at the beginning in such a way that with minimum possible expenditure it is possible to obtain two coaxial displays which both have a minimum possible inertia and thus high dynamics, and in which both pointers can be illuminated by injecting light from the side facing away from the viewer.
This problem is overcome according to the invention in that one of the pointer shafts is arranged eccentrically with respect to the two concentric scales, and the pointer assigned to the eccentric pointer shaft is embodied as an optical pointer which has a lightguide which is arranged radially on the eccentric pointer shaft and can rotate with the pointer shaft, and a lightguide system which is formed from fixed lightguides, the lightguides of which each start at a small distance from the movement path of the free end of the movable lightguide and lead to display segments on the assigned, concentric scale.
In such a pointer instrument, two coaxial displays with pointer drives which are arranged eccentrically with respect to one another are possible without two coaxial pointer shafts and a gear mechanism for bridging the distance between the eccentric pointer drive and the pointer shaft assigned to it being required. For this reason, the same display dynamics can be achieved as in a pointer instrument with scales which are arranged eccentrically with respect to one another. Furthermore, the illumination of the two pointers by injecting light does not present any difficulties. Because, in comparison with a pointer instrument with eccentric pointer shafts and eccentric scales, the pointer instrument according to the invention does not require any additional gear mechanism to bridge the distances between the two pointer drives, the pointer instrument according to the invention can be manufactured cost-effectively and does not require any increase in the masses which have to be set in motion in order to carry out a display process.
It is advantageous if the pointer which is assigned to the pointer shaft which is arranged coaxially with respect to the scales is embodied as a mechanical pointer which is mounted on the coaxial pointer shaft. In such a pointer instrument it is possible to provide a customary pointer for the primary display, therefore permitting intermediate values between the individual scale marks also to be read in a customary way. In contrast to this, in the optical display, only light segments which are successive light up so that the display occurs in jumps. As a result, this display is sufficient for variables in which less precise reading of the values is sufficient.
With the optical pointer it is possible to achieve different effects if, according to another development of the invention, the fixed lightguides have different light transmitting capacities from one another. This permits display segments with different degrees of brightness or display segments with the same degree of brightness to be obtained despite different distances from the light source.
If display segments which are at different distances from the light source are to appear with the same brightness, it is possible to provide for the light transmitting capacity of the fixed lightguides to be selected such that it is higher as the length of the lightguides increases.
The light transmitting capacity can be influenced by different materials for the fixed lightguides. The light transmitting capacity can be varied particularly easily if the light transmitting capacity is determined by different cross sections of the fixed lightguides.
The pointer instrument is of particularly simple design if the fixed lightguides each have a region which extends approximately parallel to the front side of the pointer instrument, and lead, with a bent portion on their radially outer side, to one display segment each of the inner scale.
Depending on the respective measurement variable, in the pointer instrument according to the invention different scale markings are illuminated when the display segments are embodied as scale markings.
Here, it is also possible to provide for the display segments to be colored differently. As a result, it is possible to illuminate critical states, for example the point where a residual quantity is reached in a fluid gauge display, by means of an appropriate color selection.
Another development of the invention comprises embodying at least one display segment as a warning display field. In such a case, the rotatable lightguide could be pivoted, by appropriately actuating the pointer drive display, in such a way that it illuminate a desired display field via the corresponding, fixed lightguide, and as a result, for example, an optical warning for excessively low oil pressure or for excessively high water temperature of the engine appears.
For application in a motor vehicle it is particularly advantageous if the mechanical pointer is part of a tachometer of a motor vehicle, and the optical pointer is part of a revolution counter of a motor vehicle.